revisiting nutev -or- what kevin did last week kevin mcfarland rochester neutrino group meeting 21...
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Revisiting NuTeV-or-
What Kevin Did Last Week
Kevin McFarlandRochester Neutrino Group Meeting
21 February 2011
The Big PictureNeutrinos are important in electroweak physics– there is a glorious history, of course…– … but precision today in neutrino electroweak
couplings lags behind other sectorsneutrino couplings are the most difficult couplings to measure precisely at the Z0 pole
matter effects in ν oscillations are sensitive to only flavor non-diagonal couplings
Some outstanding puzzles in neutrino physics– ~3σ NuTeV result σ(νq→νq)/σ(νq→μq’)– ~2σ deficit in “Nν” LEP measurement of Γ(Z0→νν)
– To date, only ~5% precision on σ(νe→νe)
21 February 2011
1984
• Walter Mondale asks “where’s the beef”?• KSM takes driver’s education• FNAL-E744 (CCFRW) takes data
1993
• William Jefferson Clinton becomes President• KSM plays minor role in production of his first offspring, who today wants to take driver’s ed• NuTeV Experiment proposed to recycle CCFR detector with a new beamline
1996
• William Jefferson Clinton invites an intern back to see his cigar collection• KSM analyzes E744 (and E770) data to measure NC/CC• NuTeV takes first beam
1997
• Father of one of KSM’s pothead buddies from college with cartoon last name finds himself looking blue dress DNA• NuTeV data taking complete
2001
• Men with box cutters kill thousands. US begins self-destructive response• KSM presents NuTeV results “A departure from prediction” at Fermilab Wine and Cheese
2002
• Last “Saddam [yes]” election• MINERvA and T2K proposed (leaving to later immitation “Saddam [yes]” style elections)• “The NuTeV-a result-a, she ees-a sheet-a” – Quote from Theorist, whose last name begins with one of “DGLAP”
NuTeV Revisited, K. McFarland 421 February 2011
Measure n NC/CC ratio to extract ratio of weak couplings– ratio is experimentally and theoretically robust– largest uncertainty: suppression of charm production in CC (mc)– can extract sin2qW. NuTeV measurement often quoted this way.
With neutrino and anti-neutrino beams, can form
NuTeV Measurement Technique
(3) 2Coupling sinweak em WJ Q (3)Coupling weakJ
Charged-Current(CC)
Neutral-Current(NC)
0
Only valence quarks contribute
(in particular, cancels )
sea seaq q
s c s c
2 2 2, , ,L R L R L Rg u d
2 2 2 212
Paschos - Wolfenstein Relation
sinNC NCW L R
CC CC
R g g
NuTeV Revisited, K. McFarland 521 February 2011
Beam identifies neutral currents as n or n(n in n mode 310-4, n in n mode 410-3) Beam only has ~1.6% electron neutrinos Important background for NC
events since no final state muon
NuTeV Sign-Selected Beamline
Dipoles make sign selection - Set /n n type - Remove ne from KL (Bkgnd in previous exps.)
2 212
Paschos - Wolfenstein Relation
sinNC NCW
CC CC
R
NuTeV Revisited, K. McFarland 621 February 2011
exp exp
2 2
2exp exp
large smallsin sin
sin systematics (i.e. )W W
W c
dR dR
d d
R R m
Paschos-Wolfenstein à la NuTeV( )
( )
( )( ) 2 2 4
0( )
1 5sin sin (1 )
2 9CC
CC
NCW W
CC
R
2 ( ) sin 0.22770.0013( .)0.0009( .)
on shellW
statsyst
NuTeV result:– Statistics dominate uncertainty
EWK fit (LEPEWWG 2001): – 0.2227 0.00037, a 3s discrepancy
exp
exp
0.3916 0.0013 ( : 0.3950) 3
0.4050 0.0027 ( : 0.4066)
R SM difference
R SM Good agreement
NuTeV fit for sin2θW
and mc given external constraint from strange sea
analysis. (More later)
QCD SymmetryViolations
What symmetry violations can affect the result?
1. u≠d in target (neutron excess)
2. asymmetric heavy seas
NuTeV Revisited, K. McFarland 821 February 2011
Symmetry Violating QCD EffectsPaschos-Wolfenstein R- assumptions:– Assumes total u and d momenta equal in target– Assumes sea momentum symmetry, s =s and c =c– Assumes nuclear effects common in W/Z exchange
To get a rough idea offirst two effects, can calculate them for R-
2 2
2 2
2 2
2 2 2
3
13
2
2 (3 )
u d
v vu d
v v
v vu d
v v
d u d cv v
R
U DN
U D
U D
U D
S
U D
2 22 , ,,
( )where
( ) , etc.
( ) , etc.
( )
kinematic charm CC suppression
p pv v v
p nv v v
u d u du d L R
c
N ZN
AU x u d dx
U x u d dx
S x s s dx
Asymmetric Strange Sea
1. Why it might be so
2. How it is measured at NuTeV This is what drives us to update the
NuTeV measurement
NuTeV Revisited, K. McFarland 1021 February 2011
A Very Strange Asymmetry
Perturbative strange sea is (roughly) momentum symmetric…
But “intrinsic” strange sea need not be!– so is a DIS probe of intrinsic
strangeness!– Brodsky first suggested it! (though this
model at right is excluded by NuTeV data) Brodsky and Ma, Phys. Let. B392
Paschos-Wolfenstein relation assumes that strange sea is symmetric, i.e., no “valence” strange distribution– if there were on, this would be a big deal since it is an
isovector component of the PDFs(charm sea is heavily suppressed)
~30% more momentum in strange sea than in half of strange+anti-strange seas would “fix” NuTeV sin2θW
Why might one think that the strange and anti-strange seas would be different?
G.P. Zeller et al., Phys.Rev.D65:111103,2002)
( ) ( )s x s x
NuTeV Revisited, K. McFarland 1121 February 2011
How Does NuTeV Measure This?
m± from semi-leptonic charm decay
Fits to NuTeV and CCFR n and dimuon data can measure the strange and antistrange seas separately – NuTeV separate n
and beams important for reliable separation of s ands
(Cabbibo supp.) beam: , cs d (Cabbibo supp.) beam: , cs d
( )
N X
NuTeV Revisited, K. McFarland 1221 February 2011
NEW NuTeV NLO AnalysisHave incorporated CTEQ strange “valence” evolution and CTEQ parameterizations– thanks esp. to Amundson, Kretzer, Olness & Tung
NuTeV NLO analysis (Phys.Rev.Lett.99:192001,2007) is near zero, but slightly positive– will shift central value
towards standard modeland increase uncertainties
– at NLO, with CTEQ6 as base PDF
courtesy heroic efforts of D. Mason, P. Spentzouris
(additional unc. of 0.00128 from external inputs, primarily B(c ))
( ) .00196 0.00065S x s s dx
NuTeV Update
1. Effects incorporated– Numerical Estimations
2. To do
NuTeV Revisited, K. McFarland 1421 February 2011
What’s Done?Three large effects– Estimate for Strange Sea, S-/S+~0.09±0.04
– External K+e3 branching ratio
Brookhaven E-865, famous for “fixing” the unitarity of the first row of the CKM matrix– also improves agreement with our own (less
precise) measurement of νe flux
Strong effect on our electron neutrino background
– d/u PDF uncertaintiespointed out by Kulagin and Alekhin that these were underestimated in published result
also corrected target neutron excess
NuTeV Revisited, K. McFarland 1521 February 2011
Changes in Prediction of Rν
exp
exp
0.0034 0.0013
0.0016 0.0027pred
pred
R R
R R
published:
exp
exp
0.0038 0.0013
0.0026 0.0029pred
pred
R R
R R
updated:
Rν Rνbar
Source σpub σnew Δ σpub σnew Δmtop n/a n/a +0.00001 n/a n/a -0.00015
d/u 0.00004 0.00013 +0.00000 0.00004 0.00018 +0.00000
νe 0.00028 0.00029 +0.00078 0.00062 0.00062 +0.00085
Strange PDFs 0.00023 0.00036 -0.00038 0.00052 0.00078 +0.00029
NLO QED 0 0.00013 n/a 0 0.00061 n/a
NLO QCD 0 0.00004 n/a 0 0.00043 n/a
NuTeV Revisited, K. McFarland 1621 February 2011
NuTeV 99% Conf.
Prediction
Graphical Shifts in Rν
d/u νemtop Strange Sea, S-/S+=0.09
NuTeV Revisited, K. McFarland 1721 February 2011
NuTeV 99% Conf.
Prediction
Directions of Effects not Considered(length of arrows are arbitrary)
mcShadowing (VMD) Valence Isospin Violation
NuTeV Revisited, K. McFarland 1821 February 2011
What Are you Working on Now?
Current Work is on Improving Cross-Section Model– LO to NLO QCD cross-section– Higher twist (non-perturbative) effects smaller– Can build on better fits (global!) to two muon
data to constrain charm
Base data for cross-section comes from NuTeV (previous analysis used CCFR)
It’s “the gift that keeps on giving”…
19
What if We Don’t “Fix” NuTeV?
My money is on the second symmetry violating term,
We may have discovered large (several %) isospin violation in parton distributions
21 February 2011 NuTeV Revisited, K. McFarland
2 2
2 2
2 2
2 2 2
3
13
2
2 (3 )
u d
v vu d
v v
v vu d
v v
d u d cv v
R
U DN
U D
U D
U D
S
U D
2 22 , ,,
( )where
( ) , etc.
( ) , etc.
( )
kinematic charm CC suppression
p pv v v
p nv v v
u d u du d L R
c
N ZN
AU x u d dx
U x u d dx
S x s s dx
( ) , etc.p nv v vU x u d dx